The present invention relates to a connection detection apparatus for detecting connection of an unauthorized device to communication lines in a system in which a plurality of in-vehicle communication devices, which are installed in a vehicle, communicate with one another via the communication lines, and to an in-vehicle relay apparatus.
JP 2011-255731A discloses a method for detecting abnormality of an in-vehicle device, by calculating a return loss value of an electric wave transmitted from a detection antenna, based on forward power of the electric wave and reflected power of a received reflected wave, and comparing the waveform of the newly measured and calculated return loss value with a waveform of a return loss value stored in advance.
Furthermore, JP 2007-96799A proposes a monitoring apparatus that specifies and analyses the cause of an increase in load of a communication bus in an in-vehicle network by monitoring the communication state of the communication bus, and comparing the monitoring result of the communication bus with abnormal state information stored in advance, the abnormal state information indicating past communication states of the communication bus in which abnormalities occurred.